Over half of US adults are overweight. Treatments are currently available to help these individuals lose wright, but most will regain their loss. Thus, a major problem in the treatment of obesity is prevention of weight regain. An innovative new approach that we believe may be particularly effective in preventing weight regain is the use of an interactive computerized intervention. We propose to use the Internet and e-mail to deliver an intervention that specifically focuses on a weight gain prevention and provides all of the basic components of a cognitive behavioral approach, including goal setting, self-monitoring, feedback, prompting, problem solving motivation enhancement reinforcement and social support. We believe that Internet interventions may be particularly useful for maintenance because frequent contact can be continued long-term with low cost and maximal flexibility; the anonymity may reduce embarrassment about weight gain; educational information can be provided when it is relevant to the participant; all aspects of the intervention can be individualized and tailored to the participant; data can be easily transmitted and analyzed for trends; immediate feedback can be provided to reinforces successful achievement and catch problems early; and participants can provide ongoing social support to each other. We will test this interactive computerized intervention (ICI) by recruiting 160 individuals who lost at least 10 percent of their weight in the past year. Prior studies suggest that individuals who lost weight just 1 year ago are at greatest risk of weight regain. We will purposely recruit individuals who have lost weight using various different approaches. These individuals will be randomly assigned to a no-treatment control condition or to use the ICI program for 18 months. Outcomes will be assessed at 6, 12, and 18 months. The primary outcomes will be weight change from 0 to 18 months and the proportion who regain less than 2.5 kg over 18 months. Adherence to the intervention and acceptability of the various components will be analyzed to determine the feasibility of delivering maintenance interventions via computer. The proposed ICI intervention is innovative because it explicitly focuses on prevention of weight regain; it is developed for individuals who have lost weight in a variety of ways and need help with maintenance of weight loss; it makes use of Internet and e-mail technology that has not previously been applied to the area of the weight control (and certainly not to maintenance); and uses computer technology creatively to maximize the delivery of all of the basic components of a cognitive behavioral intervention for weight loss maintenance.